1. Field of the Invention
This invention relates in general to forming elastomeric tubular articles, and in particular to a method of forming spark plug boots utilizing an extrusion process.
2. Description of the Prior Art
A spark plug boot is an elastomeric tubular member that slides over a spark plug of an internal combustion engine to serve as an insulator. One end of the boot slides over the spark plug wire, while the other end of the boot, which is larger, slides over the spark plug. There is at least one internal shoulder within the boot, and at least two internal diameters. The majority of the boots are made from silicone rubber but some are made from organic materials.
Spark plug boots are normally made by injection molding. Rubber material is loaded into an injection molding press, which injects the material into the cavity of a mold and heats to cure. The boots thus formed are stripped from the mold and subsequently frozen by nitrogen to make the boots very hard. The frozen boots are tumbled to remove flashing and scrap. After warming to room temperature, the boots will soften to the desired hardness. While this process results in high quality boots, the injection molding, freezing and tumbling steps are expensive.